High density pulp and steam mixing



Dec. 20, 1966 N. F. PUTNAM ET AL HIGH DENSITY PULP AND STEAM MIXING 2Sheets-Sheet 1 Filed March 27 1963 N. F. PUTNAM ET AL 3,293,118

HIGH DENSITY PULP AND STEAM MIXING Dec. 20, 1966 2 Sheets-Sheet 2 FiledMarch 27 1963 United States Patent O 3,293,118 HIGH DENSITY PULP ANDSTEAM MlXiNG Neil F. Putnam and Oscar Luthi, Nashua, N.H., assignors, bymesne assignments, to Improved Machinery Inc., Nashua, N.H., acorporation of Delaware Filed Mar. 27, 1963, Ser. No. 268,251 3 Claims.(01'. 162-236) This invention relates to the heating and mixing of woodpulp, cellulose or the like with steam and more particularly to themixing of high concentrations or densities of chemically treated pulpwith injected steam in a continuous flow fashion as distinguished frombatch mixing processes.

The basic problem in the continuous mixing of steam and pulp is toexpose enough surface area of the pulp and chemical mixture to theinjected steam so as to condense all of the steam and heat the entirepulp mass within the time available in the process. This time isgoverned, of course, by the ratio of the mixing chamber volume to thethrough-put rate of the pulp. In presently known equipment, if the pulpthrough-put rate is conducted slowly enough to give the steam time topenetrate and heat throughout the moving pulp, the entire process isunduly delayed. In pulp and steam mixers of known design an increase ofspeed of operation or pulp feed may result in uneven or incompleteheating of the pulp and insuflicient condensation of the steam withinthe reduced time then available. High density pulps emphasize theseproblems.

One object of the present invention is to provide equipment and a methodfor the continuous mixing of steam with high density pulp at fasterrates than heretofore, so that-the time of the process may be shortened.A further object is to provide equipment in which the high speed heatingand mixing of steam in pulps may be carried out in such a fashion thatthe injected steam is distributed evenly and diffused thoroughlythroughout the pulp before the pulp is further processed. Improvedresults in less time are therefore sought according to this invention.

A special object of this invention is to provide steam inlet means whichwill be closed when the steam supply is discontinued, thus preventingplugging of the steam supply source with pulp.

These and other objects are met, according to a preferred embodiment ofthe invention, by providing a mixing chamber in the general form of ahollow cylinder with a rotary pulp impeller shaft mounted axiallytherein. The pulp enters near one end of the cylinder, is fed underpressure forward or longitudinally initially therein, and may be movedpast a liquid chemical injector introducing activating materials intothe pulp. When this has been accomplished the pulp is given a rotarymotion in a single transverse plane in the chamber normal to thelongitudinal pulp flow, and, at the outer edge of this plane of rotarymovement of the pulp, steam is introduced in a thin sheet from theperiphery of the casing toward the central rotor. This steam ispreferably at super atmospheric pressure and is fed from an outerannular steam jacket which has been heating the pulp while it wasprogressing toward the area of circumferential steam injection. Therotation of the pulp means that a rapidly rotating interface of the pulpis continuously exposed to the sheet of steam, producing alternatelayers of pulp and steam, thus insuring adequate exposed surface area toaccomplish complete and rapid condensation of the steam and consequentlyrapid heating of layers of the pulp. A novel pivoted-gated valve ring isprovided to inject the steam but to close the steam jacket in case thesteam supply is discontinued and lowered pressure from condensation inthe jacket or other causes should threaten entry of pulp and plugging ofthe steam inlet. The steam admission zone preferably is followed bymeans to check pulp rotation and break up the layers of steam and pulpwhich were formed upon introduction of the steam, and the steamed pulpmixture may then be worked further in the chamber or immediatelydischarged for further processing.

Other objects and further details of that which is believed to be noveland included in this invention will be clear from the followingdescription and claims, taken with the accompanying drawings in which isillustrated an example of mixer embodying the present invention andincorporating the steam injection features and method describedgenerally above.

In the drawings:

FIG. 1 is a vertical sectional view taken longitudinally through amixing apparatus or chamber according to a preferred form of theinvention;

FIG. 2 is a vertical sectional view transversely of the mixing chamberof FIG. 1 substantially on the line and in the direction of the arrows22 thereof, and

FIG. 3 is a similar vertical sectional view transversely of FIG. 1substantially on the line 33 thereof.

In carrying out the objects of this invention, in one embodimentthereof, a mixing chamber is provided in the form of a hollow cylinder10 closed at its ends 12 and 14 and carrying a rotatable impeller shaft16 which extends centrally and axially through the entire chamber. Nearone end of the mixing chamber shell a pulp inlet opening 18 is providedand a suitable outlet opening 20 is located near the other end. inlet 18is conveniently arranged above the chamber and the outlet 20 is at thebottom of the other end of the chamber. However, by making the totalchamber out of several separate flanged sections as indicated, thedirection of either the inlet or the outlet may be changed by rotationof the various sections relative to one another.

If desired, pulp may be pressure-fed through the inlet into the chamberby means of an external thick-stock pump of known design (not shown)which will introduce the pulp under pressure and force it through thechamber and out of the outlet. On the other hand, the pulp might be fedby gravity through the inlet and for that purpose, as shown in thedrawing, a series of helical feeding or conveyor screws 22 on theimpeller shaft 16 are used to impart the desired longitudinal forwardmotion and exert pressure on the pulp from the inlet through thechamber, to the outlet. In any case, means is provided for impelling thepulp to move or flow longitudinally in the chamber under pressure.

The flights of the conveyor screw immediately opposite the inlet may beprovided with external notches 24 to catch or grab any lengthyunshredded stock or fiber bundles in the pulp which might bridge overthe inlet and block the free entry of further pulp to the chamber. Also,if desired, the interior walls of the chambers may be provided withspiral rifiing ribs 26. These ribs can be used to prevent an undesirableamount of gross rotation of the pulp mix within the chamber where suchrotary motion is not desired. They may be so arranged as to assist orimpede rotation of the pulp mass to any desired degree depending uponthe circumstances of each particular installation.

In cases where liquid bleach or other chemical is desired to beintroduced, the liquid may be injected through a transversely arrangedinlet pipe 28 having a series of liquid feeding inlet openings 30therein facing in a downstream direction considering the generalprogress of pulp through the mixing chamber. The bleach or otherchemical is thus introduced under pressure in a transverse lineextending chordally of the cylinder near the impeller In the form shown,the

shaft across approximately a full diameter of the chamber. The pulp atthis point or closely adjacent it may be rotated as by a series ofradially extending curved vanes 32 fixed to the impeller shaft 16 sothat as the chemical liquid is introduced it will be spread in helicallayers or sand wiches throughout the pulp.

Following the introduction of chemicals, where such chemical addition isdesired, most or all of the rotary motion of the pulp may be stopped orchecked by inwardly radially extending curved vanes 34 secured to theWalls of the chamber. These also serve to break up layers of pulp andchemical previously introduced. It will be understood that the primarypulp impelling means, either the screw conveyor 22 or an external pumpor 'both, is causing the pulp to move generally longitudinally underpressure in the chamber at all times.

The diametrical or crosswise introduction of liquid chemical in a pulpmixer is taught by the copending patent application of Rohe V.Pennington, Jr., and John P. Rioh entitled, High Density Pulp Mixing,Serial No. 268,250, filed March 27, 1963, and assigned to the sameassignee as the present invention and application.

Outside the mixing chamber an annular steam chamber or jacket '36 isprovided by an outer annular wall 37, and steam at super-atmosphericpressure is fed to the jacket as through a steam feed inlet 38 connectedto a suitable source. The steam jacket not only heats the walls of themixing chamber and thus transfers heat to pulp moving in contact withthe walls of the mixing chamber while the pulp is being fedlongitudinally and agitated, but the temperature of the steam in thejacket is being reduced by this heat exchange process. Beyond the steamchamher the mixing chamber is enlarged as at 39 to match the diameter ofthe annular wall 37. The downstream end of the annular steam chamber 36is a discharge end in communication with the mixing chamber. It is heldopen as by spacer blocks 40 extending at intervals around the outer wallof the mixing chamber proper and the inner circumference of the annularwall 37.

- According to this invention steam under pressure is introduced allaround the periphery of the mixer casing at this end of the steamchamber, through a novel pressureactuated, pivoted-gate valve membershown here as a thin flexible metallic ring or flat annular plate 42covering the discharge end of the steam jacket, loosely held at itsouter edge in a supporting groove 44, which may be provided in one ofthe flanges 46 connecting sections of the casing together. The innercircular edge of the flat ring 42 is free and unsupported. Steam undersuperatmospheric pressure in the annular chamber will flex the thin ringplate 42 about its outer edge in one direction and swing the free inneredge of the ring to provide a slit opening 48 circumferentially of themixing chamber for the admission of steam in a thin sheet. The reasonthe outer edge of the ring 42 is loosely held and not clamped firmly inplace is that the force required to flex or swing the ring (and thusopen the valve) and the resulting stress in the ring plate due to thisrotation, are far less with a loosely held outer edge than with aclamped edge. In the event that a large amount of back pressure is builtup in the pulp in the mixing chamber, or if the pressure of the steam inthe annular steam chamber otherwise should drop below the pressure ofpulp in the mixing chamber, the ring 42. would flex or swing reverselyto cause its inner edge to close the circumferential steam opening andprevent the back flow of pulp into the steam jacket. The normal actionof the ring plate 42 will be to keep the slit 48 open to a degreesuitable to maintain injection of steam at a desirable pressure orvelocity. In the use of equipment of this nature this valving action isimportant and if the outer edges of the ring were clamped, the highforces and high stresses involved would make this type of steamadmission valve impractical.

In order to take full advantage of the circumferential inlet for steam,there is provided, immediately transversely adjacent the circumferentialopening 48, a series of radially extending curved vanes 50 which aresecured to the impeller shaft 1-6 and rotate at high speed therewith.The effect of these rotary vanes 50 is to provide a constantly changingbroad surface transversely of the chamber where the incoming steam andmoving pulp will come into contact with each other to condense thesteam. Multiple layer sandwiches of pulp and steam result. The curvatureof the vanes 50 imparts some longitudinal motion to the pulp as well asrotary motion at this point and the rotary motion or component of thepulp movement is shortly thereafter impeded by a series of radiallyinwardly extending fixed curved vanes 52 secured to the inner walls ofthe mixing chamber. When rotary pulp motion is stopped by the vanes 52,the alternating layers of pulp and steam are broken up and the steamdistributed in the pulp more completely than if the rotary motioncomponent were continued.

Thereafter the pulp may be worked or kneaded within the mixing chamberby appropriate elements carried by the rotary impeller shaft or, asshown, the heated pulp may be broken up further and directed to theoutlet by bridge-breaker impeller blades 54 carried by the rotary shaft.With this arrangement, further Working of the pulp, if necessary, isaccomplished by other equipment beyond the mixing chamber.

It will be noted that the mixing chamber illustrated consists of threezones, an inlet zone, a compaction zone and a steam introduction zone.The inlet zone receives either gravity fed or pressurized stock and thescrew flights in this zone are notched to prevent bridging of unshreddedstock. The compaction zone is equipped with spiral rifiing on the insideof the mixing chamber shell to insure complete filling of the annularspace between the rotor core and the shell and to control the speed ofadvance and rotation of the stock. The pitch of the rifling is arrangedto permit rotation of the stock mass at approximately one-half the speedof the rotor. As the stock enters the steam injection zone itsrotational velocity is increased to approach that of the rotor itself atthe place where the steam is circumferentially introduced. The curvedrotating vanes and stationary vanes alternately accelerate anddecelerate the stock to reorient the mixture and disperse the steam andchemical in the pulp.

The apparatus above described will perform the steps of: first, movingand compacting the pulp mass longitudinally in a cylindrical mixingchamber; second, heating the pulp at the walls of the chamber by heatexchange contact therewith while it is moving; third, injecting steamunder pressure from the entire periphery of the chamber in a thin sheetextending in a plane normal to the direction of longitudinal advance ofthe stock; fourth, while at the same time rapidly rotating the pulp inthe plane of steam injection so as to form successive constantlychanging helical contact surfaces between pulp and steam; and fifth,collapsing and crumbling the successive contact surfaces by stopping orchecking the rotational motion of the pulp in the chamber beforedischarge.

The heating of the pulp by steam introduced all the way around thechamber insures adequate exposed pulp surface area to accomplishcomplete and rapid condensation of the steam and thorough rapid heatingof the pulp. The rapid rotation of the pulp while the steam is beinginjected, followed by the checking of the rotational motion of the pulp,insures a uniformity of heating that is not equalled by otherarrangements. The entire process is thus completed within asubstantially shorter time and smaller space than has previously beenconsider-ed necessary.

The valve construction described above may be useful in controllingfluid flow for other applications than the pulp and steam mixing chamberhere shown. However, it has particular utility as a pressure-actuated,pivotedgate annular valve control for introducing steam or other fluidfrom a pressure chamber around the circumference of a cylinder, pipe orsimilar receptacle.

As will be evident from the foregoing description, certain aspects ofthis invention are not limited to the particular details set forth andit is contemplated that various and other modifications and applicationsof the invention will occur to those skilled in the art. It is thereforeintended that the appended claims shall cover such modifications andapplications as do not depart from the true spirit and scope of theinvention.

What is claimed as new and is desired to be secured by Letters Patent ofthe United States is:

1. Apparatus for heating a pulp mass with steam, comprising alongitudinally extending cylindrical mixing chamber having a pulp inletopening near one end and a pulp outlet opening near the other end,

means for feeding pulp under pressure longitudinally of said chamberfrom said inlet, through said chamber, to said outlet,

a presure-actuated, pivoted-gate annular valve member surrounding saidchamber for injecting steam under pressure and directing said steam insaid chamber from the entire circumference thereof towards its center ina plane transverse of the chamber, said valve member comprising aflexible flat annular valve member covering said open end of said steamjacket,

said annular valve member being loosely supported at its outer edge insaid mixing chamber, the inner edge of said valve member being free toflex under pressure to open said end of said jacket for peripheralinjection of steam under pressure therefrom into said chamber directedin a plane transversely thereof,

a set of radially extending vanes rotating in said trans verse plane forimparting a rotary component of pulp movement at the location ofcircumferential steam injection, whereby alternating layers of pulp andsteam are produced, and

a set of fixed vanes in said chamber beyond said rotating vanes, forchecking rotary movement of the pulp, whereby the layers of pulp andsteam are broken up.

2. Apparatus for heating a pulp mass and mixing it with steam,comprising a longitudinally extending cylindrical mixing chamber havinga pulp inlet opening near one end and a pulp outlet opening near theother end,

means for feeding pulp under pressure longitudinally of said chamberfrom said inlet, through said chamber, to said outlet,

a cylindrical jacket for steam under pressure surrounding a part of saidmixing chamber,

said jacket having a discharge end in communication with thecircumference of said mixing chamber,

a flexible flat ring member covering said discharge end of said jacket,and

means loosely supporting the outer edge of said ring member in saidchamber,

the inner edge of said member being free to fleX under pressure in onedirection from steam in said jacket to open said discharge end of saidjacket to said chamber around the entire circumference of the chamberand direct steam into said chamber inwardly in a plane transverse of thechamber and to flex under pressure in the opposite direction from pulpin said chamber to close said discharge end.

3. In the combination of a cylindrical receptacle and an annular fluidpressure chamber surrounding said receptacle having an annular end incommunication with the entire circumference thereof; a pressure-actuatedvalve for opening and closing said annular end to said receptacle,comprising a flat annular plate covering said annular end, and

means loosely supporting the outer circular edge of said plate,

the inner circular edge of said plate being unsupported and free to moveunder fluid pressure from the pressure chamber in one direction to opensaid annular end of said pressure chamber to said receptacle around theentire circumference thereof and to move under pressure from saidreceptacle in the opposite direction to close said annular end to saidreceptacle,

said plate, when opening the end of said pressure chamber, directingfluid from the chamber inwardly of the receptacle in a plane transverseof said receptacle.

References Cited by the Examiner UNITED STATES PATENTS DONALL H.SYLVESTER, Primary Examiner.

H. R. CAINE, Assistant Examiner.

3. IN THE COMBINATION OF A CYLINDRICAL RECEPTACLE AND AN ANNULAR FLUIDPRESSURE CHAMBER SURROUNDING SAID RECPTACLE HAVING AN ANNULAR END INCOMMUNICATION WITH THE ENTIRE CIRCUMSTANCE THEREOF; A PRESSURE-ACTUATEDVALVE FOR OPENING AND CLOSING SAID ANNULAR END TO SAID RECEPTACKE,COMPRISING A FLAT ANNULAR PLATE COVERING SAID ANNULAR END, AND MEANSLOOSELY SUPPORTING THE OUTER CIRCULAR EDGE OF SAID PLATE, THE INNERCIRCULAR EDGE OF SAID PLATE BEING UNSUPPORTED AND FREE TO MOVE UNDERFLUID PRESSURE FROM THE PRESSURE CHAMBER IN ONE DIRECTION TO OPEN SAIDANNULAR END OF SAID PRESSURE CHAMBER TO SAID RECEPTACLE AROUND THEENTIRE CIRCUMFERENCE THEREOF AND TO MOVE UNDER PRESSURE FROM SAIDRECEPTABLE IN THE OPPOSITE DIRECTION TO CLOSE SAID ANNULAR END TO SAIDRECEPTACLE, SAID PLATE, WHEN OPENING THE END OF SAID PRESSURE CHAMBER,DIRECTING FLUID FROM THE CHAMBER INWARDLY OF THE RECEPTACLE IN A PLANETRANSVERSE OF SAID RECEPTACLE.